The present invention relates to a route guidance display device for road routes capable of displaying configurations and route guidance indications for special points along the road routes such as crossroads, overhead crossing, entries to or exits from freeways, overpasses such as bridges, and underpasses such as tunnels (all hereinafter collectively referred to as "route nodes").
In recent years, display devices have been developed capable of confirming the current position of a vehicle in motion for the convenience of the driver in areas with poor signposting, etc. A route guidance display device has been proposed which brings attention to the route nodes which exist on the route which the vehicle ought to be following and makes a display of the configurations of the various route nodes together with an indication of the route the vehicle should take immediately before coming to such nodes. Examples of a device of this kind using LCD displays are noted in such publications as the Technical Report of the Television Institute, ED-409, IPD 37-12 "Liquid Crystal Display Device for Automobiles" (Nov. 17, 1978) and The Fifth International Conference on Automotive Electronics, C-201/85 (Oct. 29, 1985), "A Self-Supporting Modular Navigational System for Automobiles". In both cases, a monochrome planar radial arrow pattern is used to indicate the configuration of flat plane intersections and the direction the driver should take.
In the existing devices mentioned above there is a problem in that using an arrow pattern makes it difficult to display route nodes other than flat plane intersections, for example, the configuration of an overhead crossing point, or the direction that should be taken at such a crossing.
A variety of route guidance display devices have been proposed which give the driver advance warning of the direction to be taken at intersections and the name of the intersection. In general these consist of directions displayed on top of map data which is displayed on a display device (hereafter "display"). Other types provide a separate route guidance display device in addition to such display, but in such case the name of the intersection is not displayed.
In, for example, the route guidance display device published in Japanese Laid-Open Patent No. 1986-66920, a map is shown on the display, and as the vehicle passes through an intersection on the map, the name of the intersection is displayed on the display.
FIG. 1 shows a route guidance display device or prior art published in the above-mentioned Technical Report of the Television Institute article. In the figure, 20 is a liquid crystal pattern showing the configuration of an intersection. A liquid crystal device having this kind of display pattern is fitted on the dashboard, and is able to display the configuration of intersections and route directions only.
With such route guidance display devices in the prior art, the name of an intersection on the route is shown on the display on top of the map, and only the configuration of the intersection and route guidance are shown separately. In the above case, the driver has to read information from the display a task which is more difficult the more detailed the map is, and it takes some time to obtain the information required. Moreover, the display usually uses a CRT (cathode-ray tube), which is placed under the dashboard owing to its shape, requiring the driver to shift his line of sight considerably in order to read it while driving. On the other hand the route guidance display device shown in FIG. 1 is installed above the dashboard requiring a minimal shift in the line of sight to be read. However, since this display does not give the name of an intersection, it is difficult for the driver passing through a town with many intersections to be sure which intersection the displayed pattern actually refers to. These problems interfere with the process of safe driving.